I have a 500r and HATE it. It doesn't tell you a NUMBER for the temp that you have it set at it's just a color gradient from red (for HOT) to blue (for cold). The only thing I like about it is that you can plug in two heat sources. I hooked it up and then fiddled with the temp while watching my thermometer to try and guess which COLOR was the right temp. It turns off and on and my temps stay correct but the fact that there are no numbers infuriates me. In my opinion it is not worth the money and the Zilla thermostat I have (in the same price range) is much better. It has numbers and seems to be very effective at turning the heat source on and off as needed. The Helix thermostat that came with my GTP's cage is FAR superior but over your $100 limit.